NCERT Solutions for Class 10 Science chapter-8 How do Organisms Reproduce

 NCERT Solutions for Class 10 Science chapter-8 How do Organisms Reproduce

1. What is the importance of DNA copying in reproduction?

Solution : DNA (Deoxyribonucleic acid) is the genetic material found in the chromosomes, which are present in the nucleus of a cell. The DNA is the information site for making proteins and each specific type of protein leads to a specific type of body design.
Thus, it is the DNA molecule that determines the body design of an individual. Therefore, it can be concluded that it is the DNA that gets transferred from parents to offsprings and makes them look similar.

2. Why is variation beneficial to the species but not necessarily for the individual?

Solution : Variations are useful for the survival of species in changed environment situations. If a population of reproducing organism were suited to a particular niche and if the niche is drastically altered the population could be wiped out. However, some variations are present some species will survive. Thus, variation is useful to species but not the individual.

3. How does binary fission differ from multiple fissions?

Solution : Difference between binary fission and multiple fission :

4. How will an organism be benefited if it reproduces through spores?

Solution : The spores are covered by thick walls that protect them until they come into contact with suitable moist surface and can begin to grow.

5. Can you think of reasons why more complex organism cannot give rise to new individuals through regeneration?

Solution : Simple organisms such as Hydra and Planaria are capable of producing new individuals through the process of regeneration. The process of regeneration involves the formation of new organisms from its body parts. Simple organisms can utilize this method of reproduction as their entire body is made of similar kind of cells in which any part of their body can be formed by growth and development. However, complex organisms have organ-system level of organization. All the organ systems of their body work together as an interconnected unit. They can regenerate their  lost body parts such as skin, muscles, blood, etc. However, they cannot give rise to new  individuals through regeneration.

6. Why is vegetative propagation practiced for growing some types of plants?

Solution :

(i) Plants raised by vegetative propagation can bear flower and fruits earlier than those produced from seeds.

(ii) Such methods also make possible the propagation of plants such as banana, orange, rose and jasmine that have lost the capacity to produce seeds.

(iii) All plants produced by this method are genetically similar enough to the parent plant to have its all characteristics.

7. Why is DNA coping essential part of the process of reproduction?

Solution : DNA contains information for the inheritance of features from parents to next generation. DNA presents in nucleus of cells are the information source for making protein. If information is different, different protein will be made that lead to altered body design.

8. How is process of pollination different from fertilization?

Solution : Distinction between pollination and fertilisation:

9. What is the role of the seminal vesicles and the prostate gland?

Solution : Secretions of seminal vesicles and prostate gland provide fluid medium to sperm to move and also provide nutrition to them.

10. What are the changes seen in girls at the time of puberty?

Solution : During puberty breast size begins to increase with darkening of the skin of the nipples at the tip of breasts. Also, girls begin to menstruate at around this time.

11. How does the embryo get nourishment inside the mother’s body?

Solution : The embryo develops inside the mother's body for about nine months. Inside the uterus, the outer tissue surrounding the embryo develops finger-like projections called villi. These villi are  surrounded by uterine tissue and maternal blood. They provide a large surface area for exchange of oxygen and nutrients. Also, there is a special tissue called placenta, which is embedded in the uterine wall. The embryo receives the oxygen and nutrients from the mother's blood via the placenta. The waste materials produced by the embryo are also removed through the placenta.

12. If a woman is using a Copper-T, will it help in protecting her from sexually transmitted diseases?

Solution : Copper-T cannot protect the woman from acquiring sexually transmitted disease. It will protect her from only unwanted pregnancy.

13. Asexual reproduction takes place through budding in

(a) Amoeba

(b) Yeast

(c) Plasmodium

(d) Leishmania.

Solution : (b) Yeast

14. Which of the following is not a part of female reproductive system in human beings?

(a) Ovary

(b) Uterus

(c) Vas deferens

(d) Fallopian tube

Solution : (c) Vas deferens

15. The anther contains

(a) Sepals

(b) Ovules

(c) Carpel

(d) Pollen grains.

Solution : (d) Pollen grains.

16. What are the advantages of sexual reproduction over asexual reproduction?

Solution : Sexual reproduction leads to variation due to recombination of genetic material DNA. These variations are essential for survival of species. On the contrary, asexual reproduction does not bring about variations.

17. What are the functions performed by the testis in human beings?

Solution : In human beings, testes perform dual function:

(i) Production of sperms

(ii) Secretion of male hormone testosterone.

18. Why does menstruation occurs.

Solution : When in human female if the egg is not fertilized, it lives for about one day. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilized egg. Thus, its lining becomes thick and spongy. This would be required for nourishing the embryo if had fertilized. However, this lining is not required any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes roughly every month and is known as menstruation.

19. Draw a labeled diagram of the longitudinal section of a flower.

Solution :

20. What are the different methods of contraception?

Solution : The contraceptive methods can be broadly divided into the following types:
• Natural method— It involves avoiding the chances of meeting of sperms and ovum. In this method, the sexual act is avoided from day 10th to 17th of the menstrual cycle because during this period, ovulation is expected and therefore, the chances of fertilization are very high.  
• Barrier method In this method, the fertilization of ovum and sperm is prevented with the help of barriers. Barriers are available for both males and females. Condoms are barriers made of thin rubber that are used to cover penis in males and vagina in females.  
• Oral contraceptives In this method, tablets or drugs are taken orally. These contain small doses of hormones that prevent the release of eggs and thus fertilization cannot occur.  
• Implants and surgical methods Contraceptive devices such as the loop or Copper-T are placed in uterus to prevent pregnancy.  
Some surgical methods can also be used to block the gamete transfer. It includes the blocking of vas deferens to prevent the transfer of sperms known as vasectomy. Similarly, fallopian tubes of the female can be blocked so that the egg will not reach the uterus known as tubectomy.

21. How are the modes of reproduction different in unicellular and multicellular organism?

Solution : In unicellular organisms, cell division, or fusion leads to the creation of new individuals. In multicellular organisms with simple body organization budding, fragmentation may work but in complex multicellular organisms only sexual reproduction takes place.

22. How does reproduction help in providing stability to populations of species?

Solution : The consistency of DNA copying during reproduction is important for the maintenance of body design features that allow the organism to use the particular niche. Reproduction is, therefore, linked to the stability to populations of species.

23. What could be the reasons for adopting contraceptive methods?

Solution : The sexual act always has the potential to lead to pregnancy. Pregnancy will make major demands on the body and the mind of the woman and if she is not ready for it, her health will adversely affected. Therefore, adopting contraceptive methods are essential. Some contraceptive methods like condom also prevent spread of STDs and lethal diseases like HIV-AIDS.

 

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